In recent years there has been a great deal of work done in the field of alkali metal batteries. In particular, the work has been concentrated on the development of commercially acceptable sodium sulfur batteries for uses such as load leveling in commercial power generation plants. By load leveling it is meant that, during times of slack demand, the sodium sulfur batteries are charged by the generation equipment. In periods of high demand, the power demands are supplied not only by full utilization of the generating equipment of the plant, but also by means of discharging of the sodium sulfur batteries which were charged during off-load times.
Generally, the sodium sulfur load leveling batteries under operation conditions will work at a temperature of about 350.degree. C. The chemical elements making up the two reactants of the battery, namely, sodium and sulfur, can be extremely corrosive and, if directly mixed with one another, can produce a reaction which generates a substantial amount of heat that may be detrimental to the load leveling battery system. It is therefore very desirable to seal the reactants of such batteries securely within their containers so that they are not able to leak during operation. By preventing such leakage, corrosive attack on the battery components as well as a possible unfavorable interaction between such reactants is avoided.
It is a principal object of this invention to provide a method of initially assembling and subsequently hermetically sealing a container portion of the alkali metal battery to a ceramic portion of that battery. The method is accomplished in a expeditious manner and it provides a hermetic seal between a container portion of an alkali metal battery and a ceramic portion of such a battery which ensures that the reactant materials confined within the container will not seap through the sealed area.
The closest prior art of which we are aware is U.S. Pat. No. 4,170,694 which issued on Oct. 9, 1979 for a "Hermetically Sealed Alkali Metal Battery Container." This patent discloses a hermetically sealed alkali metal battery container which includes a ceramic ring having upper and lower contoured surfaces located on its outer circumferential surface. The battery also includes outer metal casings defining an upper battery container and a lower battery container formed so as to have a bell-shaped open end on each one. The bell-shaped open end of the respective casings are located adjacent the contoured surfaces formed on the ceramic ring. Each bell-shaped open end of a metal casing has associated therewith a sealing band which engages the open end of the casing to compress the same into engagement with an associated contoured surface of the ceramic ring to form a hermetic seal therebetween.
While the structure shown in U.S. Pat. No. 4,170,694 looks somewhat like the structure to be disclosed in this specification, the method of assembling that structure is totally distinct and different from the method specifically disclosed in this application for providing a hermetic seal between container portions of an alkali metal battery and a ceramic portion of that same battery. This total difference in the methods disclosed in the mentioned patent and in the specification following will be readily apparent after one has reviewed this specification in detail.
For the sake of full disclosure, the applicants wish to indicate that the particular patents mentioned in the Background of the Invention and Prior Art Statement portion of the mentioned U.S. Pat. No. 4,170,694 are in no way relevent to the particular method disclosed and claimed in this application. Therefore, no discussion of those patents is presented herein.